The present invention relates to an electronic device for storing and indicating illumination parameters and for controlling the exposure time in photographic cameras.
In the case of photographic cameras it is a known practice to electronically control the exposure time, possibly in direct dependence on the brightness of the object. In this method, one or more condensers which are connected in at different times depending on the exposure time are generally discharged or charged. However, it is very difficult to control the stability with regard to time of the condensers which are by necessity large. Owing to the capacitances and resistances required for time formation, limits are placed on miniaturization. The circuitry is also generally complicated by the fact that in easy to operate cameras, apart from the logarithm, the exposure time is obtained from the most varied parameters such as the intensity of illumination of the object, the aperture and film sensitivity. To obtain the exposure time itself, a "delogging" operation must be effected. If semi-conductor diodes are used for this purpose, the undesirable temperature variation of the diodes is also involved which can lead to appreciable errors. In addition, the storage and indication in analog form of a value serving as a measurement of the exposure time is a complicated method.